Rice Genomics and Genetics 2025, Vol.16, No.3, 116-131 http://cropscipublisher.com/index.php/rgg 125 5.3 Stability of soil fertility across integrated systems Although various types of rice field integrated farming systems have their own characteristics, they can all improve soil fertility and enhance its stability to varying degrees. Meng et al. (2021) quantitatively evaluated the effects of several ecological farming models in rice fields in South China on soil comprehensive fertility, including rice-fish, rice-frog, rice-duck and rice-shrimp models. The results showed that compared with single planting, the soil organic matter, total nitrogen, available nutrients and microbial indicators of these integrated planting and breeding treatments were improved to varying degrees, and the calculated soil comprehensive fertility index increased by 5% to 15%. Among them, the composite model of raising fish and ducks at the same time had the largest increase, indicating that multi-species co-cultivation has a superimposed gain effect under certain conditions. Other long-term monitoring studies also showed that integrated planting and breeding can maintain the long-term stability of soil fertility. A 10-year rice-duck co-breeding experiment conducted in Jiangxi found that the soil organic matter and nutrient content increased rapidly in the first 3-4 years, then stabilized, and remained at a plateau about 15% higher than single planting after 10 years (Teng et al., 2016). This shows that there may be a process in which the nutrient "reservoir" in the integrated planting and breeding system is gradually filled and reaches a dynamic balance. Once entering the equilibrium period, soil fertility can be maintained at a high level for a long time without fertilizer waste or environmental risks caused by continued accumulation. In contrast, due to continuous high-intensity fertilization, the soil organic matter of traditional single-season rice first increases, then often decreases and tends to decline, and the fertility stability is poor. Different animal combinations have different focuses on the impact of various soil fertility indicators. For example, the rice-duck model significantly improves the nitrogen supply of the soil, while the rice-shrimp model improves the effectiveness of phosphorus and potassium more prominently; the rice-frog model (farming frogs) can significantly increase the diversity of soil microorganisms and enzyme activity, thereby improving soil biological fertility. These differences suggest that we can choose a suitable integrated breeding model according to production needs to focus on improving certain aspects of soil fertility indicators. In general, a variety of integrated breeding models can promote the formation of higher and more stable fertility levels in the soil, and the fertility improvement effect tends to stabilize after several years of continuous operation, showing good sustainability. This is of great significance for ensuring stable grain production and long-term soil productivity. Therefore, in practice, diversified rice field integrated breeding models can be promoted according to local conditions, and the problem of nutrient accumulation that may occur in a single model can be avoided through crop rotation or model conversion, so as to achieve a long-term balance of soil nutrient dynamics. 6 Sustainability and Eco-Benefit Assessment 6.1 Reduction in fertilizer input and pollution risk The integrated rice farming model is regarded as an important way to achieve environmentally friendly agriculture. One of its major advantages is that it can significantly reduce external inputs such as fertilizers and pesticides while ensuring production. According to statistics from the national fishery technology promotion department, the average use of fertilizers and pesticides in rice-fish integrated farming fields is reduced by more than 30% compared with traditional rice fields. Taking Hubei rice-shrimp farming as an example, this model has been widely promoted in the past 10 years. The use of fertilizers in rice fields in the main crayfish production areas has decreased by about 20% compared with ten years ago, while the total rice production has increased instead of decreased. This is because shrimp feed and feces in the rice-shrimp system make up for part of the fertilizer function, while the incidence of pests and diseases has decreased, significantly reducing the application of pesticides. The direct environmental benefit brought about by the reduction of chemical inputs is the reduction of agricultural non-point source pollution load. Excess nitrogen and phosphorus in rice fields often enter the water body through leakage and runoff, causing eutrophication, and integrated farming inhibits this process. Yan et al. (2023) quantified the impact of
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